Question:

Because I was told by a friend of mine, that it's not and it's a weak hadith.

Answer:

Praise be to Allaah.

There
are saheeh ahaadeeth that indicate that the Mahdi (peace be upon him)
will appear at the end of time. He is one of the signs of the Hour.
Among these ahaadeeth are the following:

1.
Abu Sa’eed al-Khudri reported that the Messenger of Allaah (Peace &
Blessings of Allaah be upon Him) said: "At the end of the time of my
ummah, the Mahdi will appear. Allaah will grant him rain, the earth will
bring forth its fruits, he will give a lot of money, cattle will
increase and the ummah will become great. He will rule for seven or
eight years. (Mustadrak al-Haakim, 4/557-558; he said: this is a hadeeth
whose isnaad is saheeh, although it was not reported by al-Bukhaari and
Muslim. Al-Dhahabi agreed with him, and al-Albaani said: this is a
saheeh sanad, and its men are thiqaat (trustworthy), Silsilat
al-ahaadeeth al-saheehah, vol. 2, p. 336, hadeeth 771)

2.
‘Ali (may Allaah be pleased with him) said: "The Messenger of Allaah
(Peace & Blessings of Allaah be upon Him) said: ‘The Mahdi is one of
us, a member of my family. Allaah will guide him in a single night.’"
(Musnad Ahmad, 2/58, hadeeth 645, edited by Ahmad al-Shaakir, who said:
its isnaad is saheeh; Sunan Ibn Maajah, 2/1367. This hadeeth was also
classed as saheeh by al-Albaani in Saheeh al-Jaami’ al-Sagheer, 6735).
Ibn Katheer said: "This means that Allaah will forgive him, grant him
help, inspire him and guide him, when he was not like this before."
(Al-Nihaayah, al-Fitan wa’l-Malaahim, 1/29; edited by Taha Zayni).

3.
Abu Sa’eed al-Khudri said: "The Messenger of Allaah (Peace &
Blessings of Allaah be upon Him) said: ‘The Mahdi is of my lineage, with
a high forehead and a long, thin, curved nose. He will fill the earth
with fairness and justice as it was filled with oppression and
injustice, and he will rule for seven years.’" (Sunan Abi Dawud, Kitaab
al-Mahdi, 11/375, hadeeth 4265; Mustadrak al-Haakim, 4/557; he said:
this is a saheeh hadeeth according to the conditions of Muslim, although
it was not reported by al-Bukhaari and Muslim. See also Saheeh
al-Jaami, 6736).

4. Umm Salamah said:
"I heard the Messenger of Allaah (Peace & Blessings of Allaah be
upon Him) say: ‘The Mahdi is of my lineage and family, from the
descendants of Faatimah.’" (Sunan Abu Dawud, 11/373; Sunan Ibn Maajah.
2/1368. Al-Albaani said that it is saheeh in Saheeh al-Jaami, 6734)

5.
Jaabir (may Allaah be pleased with him) said: "The Messenger of Allaah
(Peace & Blessings of Allaah be upon Him) said: ‘‘Eesaa ibn Maryam
will descend, and their leader the Mahdi will say, "Come and lead us in
prayer," but he will say, "No, one of them should lead them as an honour
to this ummah from Allaah."’" The version narrated by Muslim says: "…
Then ‘Eesaa ibn Maryam (Peace be upon him) will descend and their leader
will say, ‘Come and lead us in prayer,’ but he will say, ‘No, some of
you are leaders over others as an honour from Allaah to this ummah.’"
(Reported by Muslim, 225)

6. Abu
Sa’eed al-Khudri (may Allaah be pleased with him) said: "The Messenger
of Allaah (Peace & Blessings of Allaah be upon Him) said: "He is one
of us, behind whom ‘Eesaa ibn Maryam will pray." (Reported by Abi
Na’eem in Akhbaar al-Mahdi. Al-Albaani said it is saheeh; see al-Jaami’
al-Sagheer, 5/219, hadeeth 5796).

7.
‘Abdullaah ibn Mas’ood reported that the Prophet (Peace & Blessings
of Allaah be upon Him) said: "The world will not come to an end until
the Arabs are ruled by a man from my family whose name will be the same
as mine." (Musnad Ahmad, 5/199, hadeeth 3573. Another version says: "…
whose name is the same as mine and whose father’s name is the same as my
father’s." Sunan Abi Dawud, 11/370).

The
ahaadeeth concerning the appearance of the Mahdi reach the level of
Tawaatur in meaning (tawaatur refers to a hadeeth which was narrated by
so many people through so many isnaads that it is inconceivable that
they could all have agreed on a lie). The imaams and scholars of this
ummah have stated this, and a few of their comments are quoted below:

1.
Al-Haafiz Abu’l-Hasan al-Aabiri said: "The mutawaatir reports from the
Prophet (Peace & Blessings of Allaah be upon Him) describing the
Mahdi are very many. They state that the Mahdi will be of his family,
that he will rule for seven years, that he will fill the earth with
justice, that ‘Eesaa ibn Maryam will emerge and help him to kill the
Dajjaal, and that he will lead this ummah in prayer and ‘Eesaa will pray
behind him."

2. Muhammad al-Barzanji
said, in his book al-Ishaa’ah li Ashraat al-Saa’ah: "The major signs
and the signs that will be immediately followed by the Hour: these signs
are many, of which the Mahdi will be the first. Know that the ahaadeeth
that have been narrated about him in various reports are numerous." He
also said: "You know that the ahaadeeth which speak of the Mahdi, his
appearance at the end of time, and his lineage and descent from the
Prophet (Peace & Blessings of Allaah be upon Him) via Faatimah reach
the level of tawaatur in meaning, so there is no point in denying
them."

3. Al-‘Allaamah Muhammad
al-Safaareeni said: "There are so many reports which speak of the
appearance of the Mahdi that they reach the level of tawaatur in
meaning; they are very popular among the scholars of Sunnah and have
become part of their faith." Then he quotes a number of ahaadeeth and
reports about the appearance of the Mahdi and the names of the Sahaabah
from whom they were narrated: "Many reports were narrated from the
Sahaabah whose names were mentioned and others whose names were not
mentioned, may Allaah be pleased with them all, and from the Taabi’een
after them, all of which proves that this is definitive knowledge.
Belief in the appearance of the Mahdi is obligatory, as it has been
confirmed by the scholars and is listed among the beliefs of Ahl
al-Sunnah wa’l-Jamaa’ah."

4.
Al-‘Allaamah al-Mujtahid al-Shawkaani said: "The ahaadeeth that we have
come across that speak of the awaited Mahdi reach the level of tawaatur,
including fifty saheeh, hasan and da’eef munjabar ahaadeeth. There are
mutawaatir without a doubt; indeed they are more mutawaatir than others,
according to all the standards of usool. There are also many reports
from the Sahaabah that speak about the Mahdi and that reach the level of
marfoo’, so there is no room for individual opinions in such an issue."

5.
Al-‘Allaamah al-Shaykh Siddeeq Hasan Khaan said: "Even though there are
different versions of reports concerning the Mahdi, they are so many
that they reach the level of tawaatur in meaning. They are to be found
in al-Sunan and other books of Islam."

6.
Al-Shaykh Muhammad ibn Ja’far al-Kattaani said: "The conclusion is that
the ahaadeeth narrated concerning the Mahdi are mutawaatir, as are the
ahaadeeth concerning the Dajjaal and the descent of ‘Eesaa ibn Maryam,
upon whom be peace." (See Ashraat al-Saa’ah by Yoosuf ibn ‘Abdullaah
al-Waabil, pp. 195-203).

You should
be aware that some liars have fabricated ahaadeeth about the Mahdi, and
others have even claimed to be he, or that he belongs to a group other
than Ahl al-Sunnah wa’l-Jamaa’ah. Some of these "false mahdis" have
tried to deceive the slaves of Allaah for some worldly gain and to
distort the picture of Islaam.

Some have started movements and
revolutions and gathered those people and supporters whom they were able
to deceive. Then they were destroyed, and their lies and falsehood were
exposed. None of this affects the belief of Ahl al-Sunnah wa’l-Jamaa’ah
in the Mahdi, upon whom be peace, and that he will undoubtedly appear
and rule the earth in accordance with Islamic Sharee’ah. And Allaah
knows best.